Overview
This lecture covers spermatogenesis, the process by which sperm are formed from primordial germ cells after puberty, and distinguishes it from spermiogenesis, which is the maturation of spermatids into spermatozoa.
Spermatogenesis Process
- Spermatogenesis is the process converting spermatogonia (stem cells) into spermatozoa (mature sperm).
- Primordial germ cells originate in the epiblast, move through the primitive streak to the yolk sac, then migrate to developing gonads.
- After settling in the testes, these cells multiply via mitosis and meiosis.
- Spermatogenesis only starts after puberty.
- Before puberty, spermatogonia are undifferentiated cells in the seminiferous tubules.
- Puberty initiates spermatogenesis via hormones LH (luteinizing hormone) and FSH (follicle stimulating hormone).
- LH stimulates Leydig cells to produce testosterone, which activates Sertoli cells for sperm development.
- Spermatogenesis steps: Spermatogonia (mitosis) → Primary spermatocyte (meiosis I) → Secondary spermatocyte (meiosis II) → Spermatid → Spermatozoa.
- Mitosis produces more spermatogonia, while meiosis creates genetic diversity in sperm.
- Meiosis I in males is arrested in prophase for about 22 days, then completes to produce secondary spermatocytes.
- Meiosis II produces spermatids, which undergo further maturation.
Spermiogenesis
- Spermiogenesis is the transformation of spermatids into mature spermatozoa.
- Steps of spermiogenesis:
- Acrosome formation (enzymatic cap for fertilization).
- Nuclear condensation (DNA condenses for compact head).
- Formation of neck, middle piece (with mitochondria), and tail (for motility).
- Shedding of excess cytoplasm (residual bodies).
Key Terms & Definitions
- Spermatogenesis — process of forming mature sperm from spermatogonia.
- Primordial germ cells — embryonic stem cells destined to become sperm.
- Spermiogenesis — final maturation of spermatids into spermatozoa.
- Spermatogonia — undifferentiated male germ cells.
- Primary spermatocyte — first cell to undergo meiosis in spermatogenesis.
- Secondary spermatocyte — product of meiosis I; undergoes meiosis II.
- Spermatid — haploid cell from meiosis II, matures into spermatozoa.
- Spermatozoa — mature male gametes (sperm).
- Leydig cells — cells in testes that produce testosterone.
- Sertoli cells — support cells aiding in sperm development.
- Acrosome — enzyme-filled cap on sperm head for egg penetration.
Action Items / Next Steps
- Write the steps of spermatogenesis and the pathway of germ cells for homework.
- Prepare to identify and describe the stages of spermiogenesis in detail.